While walking, humans use cyclic sequence of limb movements to move the body forward and maintain stance stability. This is accomplished by a mechanism called the double pendulum. During forward motion, the leg that leaves the ground swings forward from the hip. This sweep is the first pendulum. Then the leg strikes the ground with the heel and rolls through to the toe in a motion that can be described as an inverted pendulum. The motion of the two legs is coordinated so that one foot or the other is always in contact with the ground. Although walking is by far the most basic and common thing in life, it involves very complex mechanisms including energy storing, transfer and return which depend on a highly complex anatomical bone, muscle and tendon structure.
As a matter of fact restoring the propelling characteristics of an intact ankle-foot complex to an amputated person is a huge technical challenge in the field of engineering. From biomechanical analysis it is known that, compared to the other joints of the human body, it is the ankle that produces the most energy during locomotion. To present a quantitative indication, a 75 kg person produces a maximum joint torque of 120 Nm and a peak power between 250 and 350 W at the ankle while walking at only 3 km/h. Recreating these joint properties with a device matching the size and weight of a human foot is therefore extremely difficult and challenging. A study of the state-of-the-art in TT prostheses unfortunately shows that none of the commercially available passive devices are capable of significantly reducing energy cost of walking or enhancing prosthetic gait. Still on a research level, some powered prosthetic devices have the potential to improve amputee walking experience, but still need heavy and bulky actuators to provide the necessary power for propulsion.
Passive energy-storing-and-returning prosthetic feet present spring characteristics to improve the walking experience of amputees. A versatile and adaptive hinge joint system may be advantageous in prosthetic or orthotic devices. For example, a suitable hinge joint system may provide the possibility to naturally adapt to different walking slopes, surfaces and speeds.
In the field of orthotic and prosthetic devices, suitable hinge couplings for providing adaptable and versatile hinge joint systems are actively researched. For example, in the art the Mauch ankle is known that comprises hydraulic chambers and a gravity related opening mechanism for allowing the hydraulic fluid to flow from one chamber to the other. This type of ankle mechanism allows the artificial foot structure to adapt to different slopes. However, this mechanism has the disadvantage of lacking robustness and being susceptible to failures.
The last decades, rehabilitation engineering, and more precisely the field of lower limb prosthetics, has become a challenging context for roboticists. Many researchers have studied pathological and non-pathological gait to fully understand the human ankle-foot function during walking. These biomechanical studies and the important advances in mechatronics resulted in the development of new generation of lower limb prostheses, each aiming at, not only improving its control, comfort and cosmetics, but also reducing the psychologic stigma that society associates with the loss of a limb.
Today's prosthetic feet can be divided into conventional feet (CF), energy-storing-and-returning feet (ESR) and bionic feet. The aforementioned new generation prosthetic devices are part of the bionic feet family and can be referred to as ‘propulsive bionic feet’. The state-of-the-art in propulsive bionic feet currently consists of at least 26 devices, from which 19 have been developed in the USA, 6 in Belgium and 1 in China. Leading entities in this field are the research teams of Herr et al. (MIT—USA), Sugar et al. (ASU—USA) and Goldfarb et al. (Vanderbilt). Most of the developed devices are still on a research level, but represent a preview of tomorrow's commercial prosthetic devices. A related prosthetic foot device is disclosed in international patent application WO2011033341.
A particular problem encountered with the presently known prostheses or orthoses comprising a movement controlling mechanism (MCM), is that the MCM is not capable of fluently changing between different operational states.
Indeed, in the known prostheses or orthoses, different parts and elements of the MCM usually interact while a certain play or clearance is left between these parts or elements in order to have a sufficiently movable mechanism.
As a consequence, when such a known prosthesis or orthosis is for example used for assisting a user during walking, the user feels the change in operational status of the prosthesis or orthosis as a discontinuous event.
This is especially the case when certain parts or elements of the MCM change their movement in an opposite direction during use.
Although the actual discontinuity in the movement may occur during only a very small time gap, it has enormous consequences on the body of the user, since large forces and vibrations are introduced, which results in premature fatigue of the user.
This problem is not easy to solve since the requirement of providing a flexible and easy movement for the user is rather contradictory with the requirement of having no back-lash during changes of direction in the movement controlling mechanism.
Another disadvantage of the existing hinge joint systems is their poor energy management, which is especially the case in prostheses or orthoses of the propulsive bionic type. Therefore, there is a need for prostheses or orthoses having a more advanced movement controlling mechanism, providing a better performance during use.
While a movement controlling mechanism according to embodiments of the present invention is particularly advantageous for the use in prosthetic or orthotic devices, e.g. in prostheses, exoskeletal structures or joint assistive devices, the invention is not limited thereto.